Embodiments of the present invention generally relate to semiconductor processing systems and, more specifically, lamps for advanced heating in a semiconductor processing system.
Rapid thermal processing (RTP) systems are employed in semiconductor chip fabrication to create, chemically alter or etch surface structures on semiconductor substrates or wafers. RTP typically depends upon an array of high-intensity incandescent lamps fit into a lamphead and directed at the substrate or wafer. The lamps are electrically powered and can be very quickly turned off and on and a substantial fraction of their radiation can be directed to the substrate. As a result, the wafer can be very quickly heated without substantially heating the chamber and can be nearly as quickly cooled once the power is removed from the lamps.
An example of a RTP system is described in U.S. Pat. No. 5,155,336, which is assigned to the assignee of the present application and which is incorporated herein by reference, and includes a semiconductor processing chamber and a heat source assembly or lamphead located on the semiconductor processing chamber. A number of tungsten-halogen lamps are located in the lamphead, and the lamps are capable of heating substrates in the chamber at a rate of about 300° C./sec to temperatures as high as 1200° C. and higher. During processing, infrared radiation from the lamps radiates through an upper window, light passageways and a lower window onto a rotating semiconductor substrate in the processing chamber. In this manner, the wafer is heated to a required processing temperature.
As shown in FIG. 1, a conventional halogen lamp 10 (also referred to as a tungsten-halogen lamp) for use in semiconductor processing includes a bulb 12 (also referred to an envelope) that has a radiation generating filament in the form of a coil 14 electrically coupled between a short inner lead 16 and a long inner lead 18. Inner leads 16 and 18 are coupled to outer leads 26 by foils 22. The foils 22 are commonly made from molybdenum. The inner leads, outer leads, and foils are held in place at a lamp base 20. The lamp base is pressed together during manufacturing over the foil area to form a press seal that hermetically seals the lamp bulb. The bulb 12 is commonly made of quartz and is typically filled with a halogen containing gas.
During semiconductor processing operations, such lamps are placed in a patterned array in a processing chamber to heat a substrate placed in the chamber. The lamps operate at extremely high temperatures as noted above. Typically, about half of the radiant energy from the lamp goes out of the end of the associated light pipe after many reflections. About half of the radiant energy from the lamp is absorbed at the base 20 of the lamp and in the reflector/lamphead structure. This can cause the base of the lamp to reach much higher temperatures as compared to a lamp radiating in open space. If the base gets too hot, the average lamp lifetime can be substantially reduced. This lamp degradation is caused by rupture in the seal around the foils 22, which carry the electrical energy to the filament. Above about 300° C., the foils, which are usually made from molybdenum, are easily oxidized and the resulting molybdenum oxide causes a volume expansion which ruptures the quartz or causes an open circuit. Thus, it is necessary to provide a means for cooling the lamp base 20.
In addition, elaborate structures have been designed to conduct heat away from the lamp base 20. According to conventional methods, the lamp base 20 is encapsulated within the precision outer diameter stainless steel tube using a porous potting compound. This high precision stainless steel tube is inserted into another high precision stainless steel tube which has its outer surface (for most of its length) water cooled. A reflector sleeve which surrounds a portion of the bulb is provided to reflect radiant energy away from the bulb. This elaborate cooling mechanism causes the lamp to operate at a temperature low enough to permit long lamp life.
Another approach used to conduct heat away from the lamp is to dispose a heat shield or reflector plate within the lamp bulb between the lamp filament or coil and the lamp base. Examples of lamp bulbs that include a heat shield or internal reflector plate are disclosed in PCT International Publication No. W002/03418 and U.S. Pat. No. 6,744,187. While lamp bulbs having a heat shield or reflector plate within the bulb may be effective, these approaches require an additional part to be added to the bulb assembly.
Despite the lamp cooling approaches discussed above, it would be desirable to provide additional ways to improve heat dissipation away from the lamp, lamp base, and lamphead/reflector sleeve.